Jeremy Bentham menade att den relevanta frågan när det gäller människans behandling av andra djur är om de kan lida. Richard Dawkins anför ett skäl till varför det borde vara så att arter med låg kognitiv förmåga om något har större smärtkänslighet än arter med hög kognitiv förmåga:
I can see a Darwinian reason why there might even be be a negative correlation between intellect and susceptibility to pain. I approach this by asking what, in the Darwinian sense, pain is for. It is a warning not to repeat actions that tend to cause bodily harm. Don’t stub your toe again, don’t tease a snake or sit on a hornet, don’t pick up embers however prettily they glow, be careful not to bite your tongue. … Isn’t it plausible that a clever species such as our own might need less pain, precisely because we are capable of intelligently working out what is good for us, and what damaging events we should avoid? Isn’t it plausible that an unintelligent species might need a massive wallop of pain, to drive home a lesson that we can learn with less powerful inducement? At very least, I conclude that we have no general reason to think that non-human animals feel pain less acutely than we do, and we should in any case give them the benefit of the doubt. Practices such as branding cattle, castration without anaesthetic, and bullfighting should be treated as morally equivalent to doing the same thing to human beings.